Describing the postglacial pattern and rate of Picea expansion in Alaska using paleoecological records

Picea migration across Alaska was examined in three studies: an analysis of one paleoecological record, an assessment of stomates as a tool to detect first local occurrence, a quantification of Picea migration patterns from investigations of new metrics and uncertainty factors.; Pollen, stomates and macrofossils were analyzed with a sediment core from Jan Lake, east-central Alaska. Picea arrival at Jan Lake is within 200 years of its arrival at other AMS-dated sites across eastern and central Alaska. Evidence is found for a slight mid-Holocene Picea decline at Jan Lake, intermediate in magnitude between no decline to the east and a larger decline to the west.; Stomates were investigated as a proxy for local Picea tree presence. Stomates of Picea glauca and P. mariana could not be distinguished from one another in modern reference material. 39 surface samples were used to calibrate pollen and stomate counts for detection of local Picea; pollen and macrofossil records were supplemented with stomate counts to document Picea history. Stomates appeared in most closed forest samples; none appear in tundra surface samples. Stomates detected local Picea presence as early as or earlier than macrofossils at six fossil sites across Alaska.; Records from nine sites were chosen for quality of age control and location for analyzing Picea migration patterns. Three events were identified in each record: first local occurrence, and beginning and end of initial Picea pollen rise. Arrival dates were closely spaced among the seven eastern-most sites for the beginning of the rise (within 600 years), six sites for first local occurrence (within 1200 years), and five sites for the end of the rise (within 1600 years). Spread rates were highest among the eastern and central sites (ca. 0.5 km/year to essentially simultaneous), slower to southwestern sites (ca. 0.01 km/year or less). Highest rates of increase occurred where Picea arrival was earliest and migration was fastest, ranging from 3.3% per 100 years in eastern Alaska, to 0.1% per 100 years in southwestern Alaska. Uncertainty in age control and pollen percentages were found to be important, but do not qualitatively affect the patterns from initial observations.